Recently, owing to the emergence of IA (Information Appliance) products, touch panels have gradually replaced the traditional human-machine interfaces, such as keyboards and mice. As users can operate the touch panel easily and conveniently, the application of touch panels has expanded to the various fields, such as portable communication products and information products (e.g. PDA), banking/business systems, medical registry systems, factory-monitoring systems, public information-guide systems, and computer-aided instruction systems.
According to sensing methods, touch panels may be divided into capacitive types, sonic types, infrared types, resistive types, and magnetism-induction types. Among them, the capacitive types are applied to large-size touch panels. A capacitive touch panel comprises: an insulation substrate; an electrically-conductive layer, coated on the insulation substrate; and multiple electrically-conductive segments, printed on the electrically-conductive layer, and creating X-direction and Y-direction electrical fields. The contact of a finger or a pen point on a capacitive touch panel will create a capacitance change, which will further induce a current. According to the induced current, the X-coordinate and the Y-coordinate of the contact point can be calculated. Then, the instruction corresponding to the contact point is sent out.
U.S. Pat. No. 4,822,957 and U.S. Pat. No. 4,371,746 disclosed a touch panel; however, the electrical-field linearity thereof is unsatisfactory. The quality of the electrical-field linearity will influence the correctness of the coordinate identification of a touch panel. To solve the abovementioned problem, a U.S. Pat. No. 6,781,579 discloses a touch panel, wherein multiple rows of electrically-conductive segments are installed, and the number of the electrically-conductive segments is uneven and inward-decreases gradually. Thereby, the electrical-field linearity becomes better, and the area occupied by the electrically-conductive segments is reduced, and the usable area of the touch panel is increased.
The charge distribution of a conductor correlates with the curvature of its surface. The larger the curvature, the higher the charge density; the smaller the curvature, the lower the charge density. The abovementioned invention may improve the electrical-field linearity. However, as shown in FIG. 1, the ends of its electrically-conductive segments are rectangular, which causes the charge distribution neighboring the segment terminals to be uneven. Thus, as shown in FIG. 4B, the configuration of the electric field lines neighboring the frame will change drastically, and the electrical-field linearity neighboring the frame becomes lower, and the usable area of the touch panel is reduced.